Electrocatalytic oxidative dimerization of methane

ABSTRACT

A solid oxide fuel cell and process for direct conversion of natural gas into DC electricity concurrently with the electrocatalytic partial oxidation of methane to C 2  hydrocarbon species C 2  H 4 , C 2  H 6 , and minor amounts of C 2  H 2 .

BACKGROUND OF THE INVENTION

1. Field of the Invention

Due to the high stability of methane, it has previously been processedthrough steam reforming steps in routes to desired chemicals. Theprocess of this invention provides the direct synthesis of C₂hydrocarbons, such as ethylene, from methane by partial oxidation byelectrocatalytic oxidative dimerization of methane in the anodecompartment of a solid oxide fuel cell. The process of this inventionusing a solid oxide fuel cell is particularly suited for use incon]unction with the direct conversion of natural gas into DCelectricity concurrently with the electrocatalytic partial oxidation ofthe methane to C₂ hydrocarbon species C₂ H₄, C₂ H₆, and minor amounts ofC₂ H₂.

2. Description of the Prior Art

The complete electrochemical oxidation of methane to CO₂ and H₂ O in theanode compartment of a solid oxide fuel cell, after its initial steamreformation to hydrogen, has been used in the conversion of natural gasinto DC electricity. Handbook of Batteries and Fuel Cells, Ed. DavidLinden, 43-26 to 43-33, published by McGraw-Hill Book Company (1984).

The chemical synthesis of ethylene by oxidative coupling of methaneusing Sn, Pb, Sb, Bi, Tl, Cd, and Mn oxide catalysts is taught byKeller, G.E., and Bhasin, M.M., "Synthesis of Ethylene via OxidativeCoupling of Methane," Journal of Catalysis, 73, 9-19 (1982). However,the Keller, et al. article teaches Li, Mg, Zn, Ti, Zr, Mo, Fe, Cr, W,Cu, Ag, Pt, Ce, V, B, and Al oxides to have little or no such catalyticactivity. The chemical synthesis of ethylene directly from methane inthe presence of oxygen over LiCl-added transition metal oxide catalystsproviding high selectivity and yield is taught by Otsuka, K., Liu, Q.,Hatano, M. and Morikawa, A., "Synthesis of Ethylene by Partial Oxidationof Methane over the Oxides of Transition Elements with LiCl", ChemistryLetters, The Chemical Society of Japan, 903-906 (1986). Chemical partialoxidation of methane over LiCl--Sm₂ O₃ catalyst to C₂ products, ethyleneand ethane, with a high ethylene selectivity is taught by Otsuka, K.,Liu, Q., and Morikawa, A., "Selective Synthesis of Ethylene by PartialOxidation of Methane over LiCl--Sm₂ O₃," J. Chem. Soc., Chem. Commun.,586-587 (1986). Chemical conversion of methane to ethane and ethyleneunder oxygen limiting conditions over La₂ O₃ is taught by Lin, C.,Campbell, K. O., Wang, J., and Lunsford, J. H., "Oxidative Dimerizationof Methane over Lanthanum Oxide," J. Phys. Chem., 90, 534-537 (1986).

Oxidative coupling of methane over Ag and Bi₂ O₃ --Ag catalysts wascarried out with oxygen electrochemically pumped throughyttria-stabilized zirconia and it was found that the oxygen pumpted tothe Bi₂ O₃ --Ag catalyst showed higher catalytic activity andselectivity for the production of C₂ compounds compared to surfaceoxygen from the gas phase. Otsuka, K., Yokoyama, S., and Morikawa, A.,"Catalytic Activity--and Selectivity--Control for Oxidative Coupling ofMethane by Oxygen-Pumping through Yttria-Stabilized Zirconia," ChemistryLetters, The Chemical Society of Japan, 319-322 (1985). Electrochemicaldriving of O²⁻ species through solid electrolyte yttria-stabilizedzirconia decreased selectivity to C₂ hydrocarbons and decreases the rateof production of C₂ H₄ using an Ag-Li/MgO catalyst electrode.Seimanides, S. and Stoukides, M., "Electrochemical Modification ofAg--MgO Catalyst Electrodes during Methane Oxidation," J. Electrochem.Soc., 1535-1536, July, 1986. Rare earth metal oxides Sm₂ O₃, Ho₂ O₃, Gd₂O₃, Er₂ O₃, Tm₂ O₃, Yb₂ O₃, Y₂ O₃, and Bi₂ O₃ have been shown to havegood catalytic activity and selectivity in chemical oxidative couplingof methane, Sm₂ O₃ being the most active and selective catalyst in theformation of C₂ compounds. Otsuka, K., Jinno, K., and Morikawa, A., "TheCatalysts Active and Selective in Oxidative Coupling of Methane,"Chemistry Letters, The Chemical Society of Japan, 499-500 (1985).

SUMMARY OF THE INVENTION

This invention provides bifunctional anode electrocatalysts for solidoxide fuel cells utilizing natural gas for the production of DCelectricity concurrently with electrocatalytic partial oxidation ofmethane to C₂ hydrocarbon species, predominantly ethylene. The solidoxide fuel cell suitable for use in this invention comprises a metallicoxide oxygen reducing electronic and oxygen vacancy conductingperovskite cathode in contact on one side with an oxygen vacancyconducting solid electrolyte having high O²⁻ conductivity at fuel celloperating temperatures and an anode contacting the other side of thesolid electrolyte and comprising a metallic oxide O²⁻ conductingperovskite layer contactinq the solid electrolyte and a rare earthmetallic oxide layer contacting the opposite side of the anode metallicoxide perovskite layer, the rare earth metallic oxide layer capable ofdimerization of methane to predominantly C₂ products.

The process for concurrent production of DC current and electrocatalyticoxidative dimerization of methane in the solid oxide fuel cell of thisinvention includes passing oxygen containing gas in contact with theoutside surface of the metallic oxide oxygen reducing electronic andoxygen vacancy conducting perovskite cathode forming O²⁻. The formed O²⁻is passed from the anode to and through an oxygen vacancy conductingsolid electrolyte having high O²⁻ conductivity at fuel cell operatingtemperatures to the anode contacting the other side of the solidelectrolyte. The O²⁻ is passed from the solid electrolyte into an anodehaving a metallic oxide O²⁻ conducting perovskite anode layer in contactwith the solid electrolyte on one side and contacted with CH₄ on theother side, the anode oxidatively dimerizing CH₄ to C₂ species which arepredominantly C₂ H₄. The C₂ species and electronics are withdrawn fromthe anode region.

The anode half-cell electrocatalytic oxidative dimerization reactionsmay be generally represented by the chemical equations:

    2O.sup.2- +2CH.sub.4 →C.sub.2 H.sub.4 +2H.sub.2 O+4e-

    O.sup.2- +2CH.sub.4 →C.sub.2 H.sub.6 +H.sub.2 O+2e-

    30.sup.2- +2CH.sub.4 →C.sub.2 H.sub.2 +3H .sub.2 O+6e-

The formed ethane may then react at the O²⁻ sites to form additionalethylene. While the exact reaction mechanism is not completely known atthis time, it is not likely that unit activity oxygen is formed in theanode compartment. It is believed that the O²⁻ sites within the rareearth metallic oxide anode layer are the key to production of ethyleneas the major C₂ product.

BRIEF DESCRIPTION OF THE DRAWING

The above and further advantages of this invention will be seen inreading of the description of preferred embodiments together withreference to the drawing wherein:

FIG. 1 is a schematic representation of a solid oxide fuel cellaccording to one embodiment of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

As shown schematically in the drawing, solid oxide fuel cell 10 has ametallic oxide oxygen reducing electronic and oxygen vacancy conductingperovskite cathode 11 contacting oxygen vacancy conducting solidelectrolyte 13 through cathode/electrolyte interface 12. The oppositeside of cathode 11 is in contact with a cathode compartment for contactwith an oxygen containing gas, such as air. Means for supply of theoxygen containing gas and configuration of the cathode compartment arenot shown since any such means is suitable and well-known to the art.The oxygen is reduced to O²⁻ in cathode 11 and is passed to and throughoxygen vacancy conducting solid electrolyte 13 having high O²⁻conductivity at fuel cell operating temperatures to the anode/cathodeinterface 14. Anode 18 has metallic oxide O²⁻ perovskite anode layer 15on contact through anode/electrolyte interface 14 with electrolyte 13 onone side and on the opposite side through interface 16 with rare earthmetallic oxide anode layer 17. Rare earth metallic oxide anode layer 17is contacted with methane containing gas. The configuration andoperation of the anode compartment is not described herein since anysuitable means known to the art for contacting the outer surface ofanode 18 with methane containing gas and removing formed products fromthe anode compartment is suitable in the solid fuel cell and process ofthis invention. Oxygen vacancies, O²⁻ pass from solid electrolyte 13 toanode layer 15 wherein O²⁻ oxidation occurs with rare earth O²⁻ sitesbeing formed at the metallic oxide perovskite anode layer/rare earthmetallic oxide anode layer interfacial region 16 providing rare earthO²⁻ sites for partial methane oxidation to C₂ species comprisingpredominantly C₂ H₄ in rare earth metallic oxide anode layer 17. Asuitable current collector and external lead is provided for cathode 11and anode 18, shown as 20 and 19, respectively, to provide electronicbalance to and current withdrawal from the fuel cell.

Suitable materials for cathode 11 are electronic and oxygen vacancyconducting perovskite materials capable of reducing O₂ to O²⁻. Thecathode may comprise the following perovskite-type materials having thegeneral formula AMO₃ where A is La or Pr, M is Co, Ni, or Mn, and O isoxygen; compounds having the general formula La_(1-x) Ma_(x) MbO₃ whereLa is lanthanum, Ma is Sr, Ca, K, or Pr, and Mb is Cr, Mn, Fe, Co, orBa, and x is a number about 0.2 to about 0.01, and O is oxygen;compounds having the general formula LaMcO₃ where La is lanthanum, Mc isNi, Co, Mn, Fe, or V, and O is oxygen; and platinum. A preferredperovskite-type material for use as a cathode is strontium dopedlanthanum manganite, La₀.89 Sr₀.10 MnO₃.

Suitable oxygen vacancy conducting electrolyte 13 may comprise thefollowing compounds: Binary ZrO₂ based materials having the generalformulas ZR_(1-x) M²⁺ O_(2-x) and ZR_(1-x) M³⁺ O_(2-x/2), and ternaryZrO₂ based materials such as ZrO--Y₂ O₃ --Ta₂ O₅, ZrO₂ --Yb₂ O ₃ --MO₂,and the like, where M is Ca, Mg, Y, La, Nd, Sm, Gd, Yb, Lu, Sc, Ho, andother materials having similar physical and chemical properties, and Mcomprises from about 5 m/o to about 20 m/o; ThO₂ based materials havingthe general formulas TH_(1-x) M²⁺ O_(2-x) and Th_(1-x) M³⁺ O_(2-x/2),where M is Ca, Y, Yb, Gd, La, and other materials having similarphysical and chemical properties, and M comprises about 5 m/o to 25 m/o;CeO₂ based materials having the general formulas Ce_(1-x) M²⁺ O_(2-x)and Ce_(1-x) M³⁺ O_(2-/2x), where M is Ca, Sr, Y, La, Nb, Sm, Eu, Gd,Dy, Ho, Er, Yb, and other materials having similar physical and chemicalproperties, and M comprises about 5 m/o to 20 m/o; δ-Bi₂ O₅ basedmaterials having the general formulas Bi_(2-x) M²⁺ O_(3-x/2) ; Bi_(2-x)M⁶⁺ O_(3-x/2) ; and Bi_(2-x) M_(x) ³⁺ O₃, where M is Ca, Sr, W, Y, Gd,Dy, Er, Yb, Mo, Cr, and other materials having similar physical andchemical properties, and M comprises about 5 m/o to 35 m/o; HfO₂ basedmaterials having the general formulas Hf_(1-x) M²⁺ O_(2-x) and Hf_(1-x)M³⁺ O_(2-x/2), where M is Ca, Sr, Y, and other materials having similarphysical and chemical properties, and M comprises about 5 m/o to 35 m/o.Some suitable oxygen vacancy conducting solid electrolytes and theirconductivities are as follows:

    ______________________________________                                                                  Measurement                                                       Conductivity                                                                              Temp.                                                             (ohm.sup.-1 cm.sup.-1)                                                                    T °C.                                        ______________________________________                                        ZrO.sub.2                                                                           (15 m/o CaO)  2.4 × 10.sup.-2                                                                       1000                                        ZrO.sub.2                                                                           (8 m/o Y.sub.2 O.sub.3)                                                                     5.6 × 10.sup.-2                                                                       1000                                        ZrO.sub.2                                                                           (15-20 m/o MgO)                                                                             (2-4) × 10.sup.-2                                                                     1000                                        ZrO.sub.2                                                                           (5-15 m/o La.sub.2 O.sub.3)                                                                 (2.5-4) × 10.sup.-3                                                                   1000                                        ZrO.sub.2                                                                           (15 m/o Nd.sub.2 O.sub.3)                                                                   (1.4-3.8) × 10.sup.-2                                                                 1000                                        ZrO.sub.2                                                                           (10 m/o Sm.sub.2 O.sub.3)                                                                   5.8 × 10.sup.-2                                                                       1000                                        ZrO.sub.2                                                                           (10 m/o Gd.sub.2 O.sub.3)                                                                   1.1 × 10.sup.-1                                                                       1000                                        ZrO.sub.2                                                                           (9 m/o Yb.sub.2 O.sub.3)                                                                    1.5 × 10.sup.-2                                                                       1000                                        ZrO.sub.2                                                                           (15 m/o Lu.sub.2 O.sub.3)                                                                   1.2 × 10.sup.-2                                                                       1000                                        ZrO.sub.2                                                                           (10 m/o Sc.sub.2 O.sub.3)                                                                   2.4 × 10.sup.-1                                                                       1000                                        ZrO.sub.2                                                                           (12.7 m/o Ho.sub.2 O.sub.3)                                                                 3.5 × 10.sup.-2                                                                        880                                        ThO.sub. 2                                                                          (7 m/o CaO)   2 × 10.sup.-3                                                                         1000                                        ThO.sub.2                                                                           (15 m/o YO.sub.1.5)                                                                         6.3 × 10.sup.-3                                                                       1000                                        CeO.sub.2                                                                           (10 m/o CaO)  ≈ 10.sup.-1                                                                         1000                                        CeO.sub.2                                                                           (5 m/o Y.sub.2 O.sub.3)                                                                     ≈ 0.8 1000                                        Bi.sub.2 O.sub.3                                                                    (25 m/o Y.sub.2 O.sub.3)                                                                    ≈ 0.3  850                                        Bi.sub.2 O.sub.3                                                                    (28.5 m/o Dy.sub.2 O.sub.3)                                                                 0.14           700                                        Bi.sub.2 O.sub.3                                                                    (20 m/o Er.sub.2 O.sub.3)                                                                   1              800                                        Bi.sub.2 O.sub.3                                                                    (35 m/o Yb.sub.2 O.sub.3)                                                                   0.14           700                                        Bi.sub.2 O.sub.3                                                                    (35 m/o Gd.sub.2 O.sub.3)                                                                   0.22           700                                        ______________________________________                                    

Anode 18 has metallic oxide O²⁻ conducting perovskite layer 15contacting solid electrolyte 13 at anode/electrolyte interface 14. Anodeperovskite layer 15 may comprise any of the oxygen vacancy conductingperovskite materials set forth above for cathode 11. The perovskitematerial of the anode may be the same as or different from theperovskite material used in the cathode. Rare earth metallic oxide layer17 contacts the opposite side of anode metallic oxide perovskite layer15 at metallic oxide perovskite/rare earth metallic earth oxideinterface 16. Suitable rare earth metallic oxides for use in anode layer17 include: Sm₂ O₃, Dy₂ O₃, Ho₂ O₃, Yb₂ O₃, Nd₂ O₃, Eu₂ O₃, Er₂ O₃, Lu₂O₃, Gd₂ O₃, Tm₂ O₃, preferably Sm₂ O₃ or Dy₂ O₃.

The electrodes preferably comprise a thin electrode layer deposited onthe surface of the oxygen vacancy conducting solid electrolyte. Suitablethin electrode layers may be provided by techniques such as plasmaspraying or slurry coating followed by sintering.

Any suitable oxygen containing gas, such as air or oxygen enrichedgases, may be provided to the cathode for formation of O²⁻. Likewise,any methane containing gas, such as natural gas, synthetic natural gas,solid or liquid hydrocarbon gasification products containing methane, ormethane enriched gases may be supplied to the anode for dimerization.

One preferred solid oxide fuel cell of this invention has the generalconfiguration CH₄, Pt/Sm₂ O₃ /La₀.89 Sr.sub..10 MnO₃ /Pt/Zro₂ (8^(w)/oY₂ O₃)/La₀.89 Sr.sub..10 MnO₃ /Pt,O₂ (air).

Suitable fuel cell operating temperatures according to this inventionare about 600° to about 900° C., preferably about 750° to about 800° C.

The following examples are set forth using specific materials andprocess conditions as exemplary and for a better understanding of theinvention and should not be considered to limit the invention.

EXAMPLE I

A solid oxide fuel cell was prepared possessing the generalconfiguration CH₄, Pt/Sm₂ O₃ /La₀.89 Sr.sub..10 MnO₃ /Pt/ZrO₂ (8^(w)/oY₂ O₃ )/La₀.89 Sr.sub..10 MnO₃ /Pt,O₂ (air). The solid electrolyte wasa ZrO₂ (8^(w) /oY₂ O₃) closed-one-end oxygen conducting tube. La₀.89Sr.sub..10 MnO₃ oxygen electrodes were initially introduced into boththe anode and cathode regions of the fuel cell. These electrodes wereprepared by introducing a 5^(w) /o suspension in ethylene glycol/citricacid of La(C₂ H₃ O₂), SrCO₃ and MnCO₃ of appropriate composition ontoboth the outside and inside walls of the yttria stabilized zirconiasolid electrolyte tube. For this laboratory cell, platinum wire, 0.25mm, current collectors were initially in close mechanical contact toboth inside and outside walls of this solid electrolyte. Decompositionof the electrocatalyst precursor was achieved by heating the tubeassembly to 800° C. in air for 1 hour followed immediately by heatingthe cell assembly to 1250° C. for 1 hour to form the La₀.89 Sr.sub..10MnO₃ electrodes on each side of the solid electrolyte. In most casesgood adhesion was found between the finally sintered electrodes, thesolid electrolyte tube and the platinum current collectors. Samaria (Sm₂O₃) was introduced as a thin layer suspension in dimethylformamide ontothe inside wall electrode anode surface of the fuel cell. Estimated Sm₂O₃ loading was 20 mg/cm². The assumption was made that upon subsequentheating of this fuel cell in the atmosphere to ≈900° C., some limitedsintering or solid-state diffusion by Sm₂ O₃ into La₀.89 Sr.sub..10 MnO₃may occur at their interfacial region. It was anticipated that diffusionby Sm₂ O₃ into perovskites sites would be localized and not result insignificant changes to the bulk properties of these two materialscomprising the bifunctional anode.

EXAMPLE II

The cell of Example I was operated with anode fuel gas of 10% CH₄ inargon and the cathode oxygen source of air at flow rates of 50 ml/min.The cell was operated at 760° C. under an open-circuit potential of1.25V. Analysis of anode reaction products was performed using a GOW-MACModel 69-750 FID gas chromatograph using a 6 ft.×1/8 inch stainlesssteel column packed with 80/100 mesh Carbosphere (Alltech Associates,Inc.). No C₂ species were evident from either the methane or argonsources.

EXAMPLE III

The cell of Example I was then operated under open-circuit potential ofinitial 1.23V at 760° C. with anode gas composition of 10% CH₄ in argonwith varying oxygen concentration in the anode gas as shown in Table 1flowed at 50 ml/min. Methane oxidative dimerization to C₂ species, C₂ H₄+C₂ H₆ +C₂ H₂ was found to be dependent upon oxygen concentration asshown in Table 1.

                  TABLE 1                                                         ______________________________________                                                     Total C.sub.2 Conc. ppm                                          O.sub.2 Conc. %                                                                            (C.sub.2 H.sub.4 + C.sub.2 H.sub.6 + C.sub.2 H.sub.2)            ______________________________________                                        0.25          55                                                              0.60         135                                                              0.90         192                                                              ______________________________________                                    

EXAMPLE IV

The cell of Example I was then operated by passing current through thecell as shown in Table 2 at 760° C. with flow rates of 50 ml/min. ofanode gas composition of 10% CH₄ and 90% argon and with cathode gas ofair. Upon Faradaic transport of O²⁻ through the solid electrolyte fromthe air cathode to the anode, the total yield of C₂ species increasedand was linearly related to cell current as shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Total           Total                                                         Cell Current, (mA)                                                                            C.sub.2 Species, ppm                                          ______________________________________                                        10               90                                                           16              150                                                           ______________________________________                                    

C₂ H₄, C₂ H₆, and C₂ H₂ were identified as Faradaic methane oxidativedimerization products with a distribution of 58% C₂ H₄, 37% C₂ H₆ and 4%C₂ H₂. Eleven percent of the Faradaically transported oxygenparticipated in the methane oxidative dimerization. Anode electrodepotentials were always negative of the oxygen electrode potential, hencethe Faradaic oxidative dimerization reaction did not rely upon unitactivity oxygen being produced in the anode compartment.

While in the foregoing specification this invention has been describedin relation to certain preferred embodiments thereof, and many detailshave been set forth for purpose of illustration it will be apparent tothose skilled in the art that the invention is susceptible to additionalembodiments and that certain of the details described herein can bevaried considerably without departing from the basic principles of theinvention.

We claim:
 1. A solid oxide fuel cell for electrocatalytic oxidativedimerization of methane comprising;a metallic oxide oxygen reducingelectronic and oxygen vacancy conducting perovskite cathode; an oxygenvacancy conducting solid electrolyte having high O²⁻ conductivity atfuel cell operating temperatures with one side contacting one side ofsaid cathode; and an anode contacting the other side of said solidelectrolyte and comprising a metallic oxide O²⁻ conducting perovskitelayer contacting said solid electrolyte and a rare earth metallic oxidelayer contacting the opposite side of said anode metallic oxideperovskite layer and capable of dimerization of said methane topredominantly C₂ products.
 2. A solid oxide fuel cell according to claim1 wherein said perovskite cathode is selected from the group consistingof materials having the general formula AMO₃ where A is selected from Laand Pr, M is selected from Co, Ni, and Mn, and O is oxygen; compoundshaving the general formula La_(1-x) Ma_(x) MbO₃ where La is lanthanum,Ma is selected from Sr, Ca, K, and Pr, and Mb is selected from Cr, Mn,Fe, Co, and Ba, and x is a number about 0.2 to about 0.01, and O isoxygen; compounds having the general formula LaMcO₃ where La islanthanum, Mc is selected from Ni, Co, Mn, Fe, and V, and O is oxygenand platinum.
 3. A solid oxide fuel cell according to claim 1 whereinsaid perovskite cathode is La₀.89 Sr₀.10 MnO₃.
 4. A solid oxide fuelcell according to claim 1 wherein said electrolyte is selected from thegroup consisting of binary ZrO₂ based materials having the generalformulas Zr_(1-x) M²⁺ O_(2-x) and and ternary ZrO₂ based materials suchas ZrO--Y₂ O₃ --Ta₂ O₅, ZrO₂ --Yb₂ O₃ --MO₂, and the like, where M isselected from Ca, Mg, Y, La, Nd, Sm, Gd, Yb, Lu, Sc, and Ho and Mcomprises from about 5 m/o to about 20 m/o; ThO₂ based materials havingthe general formulas Th_(1-x) M²⁺ O_(2-x) and Th_(1-x) M³⁺ O_(2-x/2),where M is selected from Ca, Y, Yb, Gd, and La and M comprises about 5m/o to 25 m/o; CeO₂ based materials having the general formulas Ce_(1-x)M²⁺ O_(2-x) and Ce_(1-x) M³⁺ O_(2-/2x), where M is selected from Ca, Sr,Y, La, Nb, Sm, Eu, Gd, Dy, Ho, Er, and Yb and M comprises about 5 m/o to20 m/o; δ-Bi₂ O₅ based materials having the general formulas Bi_(2-x)M²⁺ O_(3-x/2) ; Bi_(2-x) M⁶⁺ O_(3-x/2) ; and Bi_(2-x) M_(x) ³⁺ O₃, whereM is selected from Ca, Sr, W, Y, Gd, Dy, Er, Yb, Mo, and Cr and Mcomprises about 5 m/o to 35 m/o; and HfO₂ based materials having thegeneral formulas Hf_(1-x) M²⁺ O_(2-x) and Hf_(1-x) M³⁺ O_(2-x/2), whereM is selected from Ca, Sr, and Y and M comprises about 5 m/o to 35 m/o.5. A solid oxide fuel cell according to claim 1 wherein said anodemetallic oxide perovskite layer is selected from the group consisting ofmaterials having the general formula AMO₃ where A is selected from Laand Pr, M is selected from Co, Ni, and Mn, and O is oxygen; compoundshaving the general formula La_(1-x) Ma_(x) MbO₃ where La is lanthanum,Ma is selected from Sr, Ca, K, and Pr, and Mb is selected from Cr, Mn,Fe, Co, and Ba, and x is a number about 0.2 to about 0.01, and O isoxygen; compounds having the general formula LaMcO₃ where La islanthanum, Mc is selected from Ni, Co, Mn, Fe, and V, and O is oxygen;and platinum.
 6. A solid oxide fuel cell according to claim 1 whereinsaid anode metallic oxide perovskite layer is La₀.89 Sr₀.10 MnO₃.
 7. Asolid oxide fuel cell according to claim 1 wherein said rare earthmetallic oxide layer is selected from the group consisting of Sm₂ O₃,Dy₂ O₃, Ho₂ O₃, Yb₂ O₃, Nd₂ O₃, Eu₂ O₃, Er₂ O₃, Lu₂ O₃, Gd₂ O₃, and Tm₂O₃.
 8. A solid oxide fuel cell according to claim 1 wherein said rareearth metallic oxide layer is selected from the group consisting of Sm₂O₃ and Dy₂ O₃.
 9. A solid oxide fuel cell according to claim 1 havingthe configuration CH₄, Pt/Sm₂ O₃ /La₀.89 Sr.sub..10 MnO₃ /Pt/ZrO₂ (8^(w)/oY₂ O₃) /La₀.89 Sr.sub..10 MnO₃ /Pt,O₂ (air).
 10. Process forconcurrent production of DC current and electrocatalytic oxidativedimerization of methane in a solid oxide fuel cell comprising:passingoxygen containing gas in contact with one side of a metallic oxideoxygen reducing electronic and oxygen vacancy conducting perovskitecathode forming O²⁻ ; passing formed O²⁻ to and through an oxygenvacancy conducting solid electrolyte having high O²⁻ conductivity atfuel cell operating temperatures to an anode contacting the other sideof said solid electrolyte; passing O²⁻ from said solid electrolyte intoan anode comprising a metallic oxide O²⁻ conducting perovskite anodelayer in contact with said electrolyte on one side and having a rareearth metallic oxide anode layer in contact with said metallic oxideanode layer on the other side and in contact with CH₄ containing gas onits other side, oxidatively dirmerizing CH₄ to C₂ species comprisingpredominantly C₂ H₄ and forming e- in said anode; and withdrawing saidC₂ species and e- from said anode.
 11. Process for concurrent productionof DC current and electrocatalytic oxidative dimerization of methaneaccording to claim 10 wherein said oxygen containing gas is air. 12.Process for concurrent production of DC current and electrocatalyticoxidative dimerization of methane according to claim 10 wherein saidperovskite cathode is selected from the group consisting of materialshaving the general formula AMO₃ where A is selected from La and Pr, M isselected from Co, Ni, and Mn, and O is oxygen; compounds having thegeneral formula La_(1-x) Ma_(x) MbO₃ where La is lanthanum, Ma isselected from Sr, Ca, K, and Pr, and Mb is selected from Cr, Mn, Fe, Co,and Ba, and x is a number about 0.2 to about 0.01, and O is oxygen;compounds having the general formula LaMcO₃ where La is lanthanum, Mc isselected from Ni, Co, Mn, Fe, and V, and O is oxygen; and platinum. 13.Process for concurrent production of DC current and electrocatalyticoxidative dimerization of methane according to claim 10 wherein saidperovskite cathode is La₀.89 Sr₀.10 MnO₃.
 14. Process for concurrentproduction of DC current and electrocatalytic oxidative dimerization ofmethane according to claim 10 wherein said electrolyte is selected fromthe group consisting of binary ZrO₂ based materials having the generalformulas Zr_(1-x) M²⁺ O_(2-x) and Zr_(1-x) M³⁺ O_(2-x/2), and ternaryZrO₂ based materials such as ZrO--Y₂ O₃ --Ta₂ O₅, ZrO₂ --Yb₂ O₃ --MO₂,and the like, where M is selected from Ca, Mg, Y, La, Nd, Sm, Gd, Yb,Lu, Sc, and Ho and M comprises from about 5 m/o to about 20 m/o; ThO₂based materials having the general formulas Th_(1-x) M²⁺ O_(2-x) andTh_(1-x) M³⁺ O_(2-x/2), where M is selected from Ca, Y, Yb, Gd, and Laand M comprises about 5 m/o to 25 m/o; CeO₂ based materials having thegeneral formulas Ce_(1-x) M²⁺ O_(2-x) and Ce_(1-x) M³⁺ O_(2-/2x), whereM is selected from Ca, Sr, Y, La, Nb, Sm, Eu, Gd, Dy, Ho, Er, and Yb andM comprises about 5 m/o to 20 m/o; δ-Bi₂ O₅ based materials having thegeneral formulas Bi_(2-x) M²⁺ O_(3-x/2) ; Bi_(2-x) M⁶⁺ O_(3-x/2) ; andBi_(2-x) M_(x) ³⁺ O₃, where M is selected from Ca, Sr, W, Y, Gd, Dy, Er,Yb, Mo, and Cr and M comprises about 5 m/o to 35 m/o: and HfO₂ basedmaterials having the general formulas Hf₁₋ M²⁺ O_(2-x) and Hf_(1-x) M³⁺O_(2-x/2), where M is selected from Ca, Sr, and Y and M comprises about5 m/o to 35 m/o.
 15. Process for concurrent production of DC current andelectrocatalytic oxidative dimerization of methane according to claim 10wherein said anode metallic oxide perovskite layer is selected from thegroup consisting of materials having the general formula AMO₃ where A isselected from La and Pr, M is selected from Co, Ni, and Mn, and O isoxygen; compounds having the general formula La_(1-x) Ma_(x) MbO₃ whereLa is lanthanum, Ma is selected from Sr, Ca, K, and Pr, and Mb isselected from Cr, Mn, Fe, Co, and Ba, and x is a number about 0.2 toabout 0.01, and O is oxygen; compounds having the general formula LaMcO₃where La is lanthanum, Mc is selected from Ni, Co, Mn, Fe, and V, and Ois oxygen; and platinum.
 16. Process for concurrent production of DCcurrent and electrocatalytic oxidative dimerization of methane accordingto claim 10 wherein said anode metallic oxide perovskite layer is La₀.89Sr₀.10 MnO₃.
 17. Process for concurrent production of DC current andelectrocatalytic oxidative dimerization of methane according to claimlu/wherein said rare earth metallic oxide layer is selected from thegroup consisting of Sm₂ O₃, Dy₂ O₃, Ho₂ O₃, Yb₂ O₃, Nd₂ O₃, Eu₂ O₃, Er₂O₃, Lu₂ O₃, Gd₂ O₃, and Tm₂ O₃.
 18. Process for concurrent production ofDC current and electrocatalytic oxidative dimerization of methaneaccording to claim 10 wherein said rare earth metallic oxide layer isselected from the group consisting of Sm₂ O₃ and Dy₂ O₃.
 19. Process forconcurrent production of DC current and electrocatalytic oxidativedimerization of methane according to claim 10 wherein said CH₄containing gas is natural gas.